VM: Support bootstrapping core libraries from Kernel binaries instead of source.

runtime/bin/gen_snapshot.cc

Index: runtime/bin/gen_snapshot.cc
diff --git a/runtime/bin/gen_snapshot.cc b/runtime/bin/gen_snapshot.cc
index 17acc09fcd58da6d6c0b6ad2c5f1da1933aa995e..5d971eff441093dc1d42738474d67860ae6aa9c1 100644
--- a/runtime/bin/gen_snapshot.cc
+++ b/runtime/bin/gen_snapshot.cc
@@ -1266,8 +1266,16 @@ int main(int argc, char** argv) {
     // Now we create an isolate into which we load all the code that needs to
     // be in the snapshot.
     isolate_data = new IsolateData(NULL, NULL, NULL);
-    if (Dart_CreateIsolate(NULL, NULL, NULL, NULL, isolate_data, &error) ==
-        NULL) {
+    intptr_t payload_bytes = 0;
+    const uint8_t* payload = NULL;
+    const bool is_kernel_file =
+        TryReadKernel(app_script_name, &payload, &payload_bytes);
+    Dart_Isolate isolate =
+        is_kernel_file
+            ? Dart_CreateIsolateFromKernel(NULL, NULL, payload, payload_bytes,
+                                           NULL, isolate_data, &error)
+            : Dart_CreateIsolate(NULL, NULL, NULL, NULL, isolate_data, &error);
+    if (isolate == NULL) {
       fprintf(stderr, "%s", error);
       free(error);
       exit(255);
@@ -1284,11 +1292,6 @@ int main(int argc, char** argv) {
     Dart_QualifiedFunctionName* entry_points =
         ParseEntryPointsManifestIfPresent();
 
-    intptr_t payload_bytes = 0;
-    const uint8_t* payload = NULL;
-    const bool is_kernel_file =
-        TryReadKernel(app_script_name, &payload, &payload_bytes);
-
     if (is_kernel_file) {
       Dart_Handle library = Dart_LoadKernel(payload, payload_bytes);
       free(const_cast<uint8_t*>(payload));